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The crystal structures of the four-membered heterocycles ( S)-(−)-4-oxo-2-azetidinecarboxylic acid (I) and 3-azetidinecarboxylic acid (II) were solved by direct methods using powder synchrotron X-ray diffraction data. The asymmetry of the oxoazetidine and azetidine rings is discussed, along with the hydrogen bonding. [ABSTRACT FROM AUTHOR]

A temperature-controlled X-ray powder diffraction experiment, complemented with TGA and DSC analysis, allowed us to follow changes in the molecular conformation and hydrogen-bond patterns of 4-piperidinecarboxylic acid. The presence of three phases is confirmed. Phase 1 represents the monohydrated form of 4-piperidinecarboxylic acid, which exists from room temperature to 359 K, where dehydration occurs. Phase 2 measured at 363 K corresponds to an anhydrous form of the acid. At ca 458 K the onset of a second, more gradual transition is observed, which ends at around 543 K. Phase 3 measured at 543 K is a hightemperature anhydrous form of the acid. The structures of phases 2 and 3 were solved from synchrotron powder diffraction data by simulated annealing using the DASH program and refined by the Rietveld method. The phase changes are accompanied by modification of the hydrogenbond patterns and of the torsional orientation of the terminal carboxylate group. This group makes a 49° rotation about the C1-C2 bond during the first transition. [ABSTRACT FROM AUTHOR]

The article focuses on the crystal structure of the organic compound trans-Decahydronaphthalene or decalin which has been solved and refined using X-ray powder diffraction data. According to the authors, the organic compound has a variety of applications in research and industry, from multipurpose solvent to a hydrogen-storage medium for fuel cells. It notes that the location of the trans-decalin molecule is on an inversion centre with both rings in a chair conformation. Also cited is that the organic compound crystallizes easily without hydrogen bonds.